This invention relates to integrated circuits for performing a two's complement multiplication or an unsigned magnitude multiplication, and more particularly, to a method and apparatus for modifying a two's complement multiplier to also perform unsigned magnitude multiplication.
When implementing logic with integrated circuit (IC) technology, the end use of the circuit often dictates specific speed and size requirements. Accordingly, an implementation providing efficient use of silicon area while achieving the requisite speed requirements is needed. Thus, rather than include both a two's complement multiplier and an unsigned magnitude multiplier on the same IC, a more efficient solution is to include a multiplier which can perform in either format. Such a solution is desireable only if the silicon area required is less than the total area required for the two multipliers individually and the decrease in speed, if any, is within acceptable constraints.
Applications which require both two's complement operations and unsigned magnitude operations include the processing of video signals. Both formats are needed because the luminance component of the video signal is in unsigned magnitude format, while the chrominance components are in two's complement format.
A conventional approach for implementing both a two's complement multiplier and an unsigned magnitude multiplier is to use a larger multiplier than needed. Thus, a nine-bit multiplier would be used for eight-bit applications, thereby providing the capability for both eight-bit two's complement operations and eight-bit unsigned magnitude operations. The use of a larger multiplier, however, has a significant negative impact on the speed of operation and the amount of silicon area required for implementation in an integrated circuit.
Accordingly, there is a need for a multiplier implemented on an integrated circuit which can operate effectively in both two's complement format and unsigned magnitude format with little or no speed loss and minimal increase in silicon area.